Advanced Power Plant Library : User Manual

This is a preliminary version of the user documentation for APP_Lib based on the user manual for desktop installations. Some information may still refer to IPSEpro-PSE.

1. Introduction

The Advanced Power Plant Library

The Advanced Power Plant Library has been designed for modeling a wide range of thermal systems. It allows you to design and analyze any power plant, including:

Combined-cycle plants
Cogeneration plants
Conventional plants

The library contains models for both design and off-design analysis.

The way that the Advanced Power Plant Library was designed, using the Model Development Kit (MDK) of IPSEpro, allowed the creation of extremely powerful component models.

The component models are formulated in a way that virtually all of them can be used in connection with a wide range of working media. This way, it is not necessary to distinguish between a compressor for gas, fuel or steam. The compressor model uses correctly the working fluids of the connected streams.

About this Manual

This documentation describes the Advanced Power Plant Library. It provides information for both new and experienced users of IPSE GO. For a comprehensive description about IPSE GO, refer to the IPSE GO User Documentation.

If you are a new user, you find in this documentation a series of examples created with the Advanced Power Plant Library. These examples explain you how to set up a power plant model. It also shows how the system reacts on the most frequent input errors.

If you are an experienced user of IPSE GO, you find in this documentation information about some aspects that are specific to the Advanced Power Plant Library.

This manual contains the following chapters:

Chapter 1 introduces the Advanced Power Plant Library and establishes the assumptions and conventions used in this documentation.

Chapter 2 describes the design considerations and the available components of the Advanced Power Plant Library.

Chapter 3 provides information about the physical properties and the chemical compositions used in the Advanced Power Plant Library.

Chapter 4 shows various examples of process models in IPSE GO, using the Advanced Power Plant Library.

Conventions

This documentation uses the following definitions and typographic conventions:

Definitions

process scheme, flowsheet: The graphical representation of your project in your IPSE GO project window is called process scheme, or flowsheet.

model, process model: The mathematical representation of a process scheme is called process model, or just model.

project: A project is the collection of all available information about a process model.

unit icon: The graphical representation of a component of a model library, available for building a process scheme, is called unit icon or just icon.

component model, component: The mathematical representation of a library component, within a process model, is called component, component model, or just model (whenever its meaning does not conflict with process model).

object: All elements contained in a project are called objects. Besides component models, connections and compositions, additional objects, such as data frames and reference crosses can be used in a project.

Typographical Conventions

As far as possible, this documentation uses the same typographical conventions as the Windows documentation. In particular, the following typographical conventions are used throughout this documentation:

Style

Meaning

Italic

Indicates a placeholder for information. For example, if you are asked to type filename, you must type the actual name of the file instead of the italic printed word.

Bold Italic

Indicates text that must be entered exactly as printed.

It also indicates new terms. The explanation follows immediately after the term printed bold italic.

ALL UPPERCASE

Directories, filenames

File › Save

Commands that you can access via the menu

Button

Commands that you can access by clicking on a button

Key name

Key names - for example Ctrl-Key, Del-Key.

[[optional]]

Expressions in double brackets are optional

Keyboard Conventions

The key names in this documentation appear key symbols. For example, the shift key appears as Shift.

A plus sign (+) between key names means that you must press the keys at the same time. For example, Shift+F1 means you press and hold down Shift while you press F1.

A period ( , ) between key names means that the keys must be pressed sequentially. For example, Alt, E, O means you first press and release Alt, then press and release E, and finally press O.

2. Library Overview

This chapter introduces the design considerations of the Advanced Power Plant Library.

Design Considerations

The Advanced Power Plant Library has been implemented with the aim of allowing the modeling of a wide range of thermal power plants. The library models have been carefully chosen, to provide maximum flexibility for the user. For example, most units can be used for all available working media. In this way, it is not necessary to use different models depending on the working fluid that is adopted by the project. This feature reduces considerably the number of required components in the library, and makes it easy to add new working fluids when required.

In the course of a project, you will frequently have a varying demand on the component models that you are using. In the beginning of the project, it is usual to have only preliminary data available to feed the component models. At this stage you will, most likely, prefer to use relatively simple models.

For each library unit of the Advanced Power Plant Library, a default model is available, which guarantees fast results in the simulation phase. In order to achieve this, the following aspects have been taken into account:

Minimal data input required by the user.
Simple mathematical formulation in order to achieve fast convergence.

When you select a library unit to become a new object of your process model, this object automatically uses its built-in default model.

If required, you can switch to another model of that unit. For example, you may wish to use the model for off-design calculations. You can also base your off-design models on results obtained with the design model of the process.

Off-Design Behavior

Specialized off-design models are available for each unit of the Advanced Power Plant Library.

While the design models focus on few data input and on fast convergence, the off-design models emphasize the following aspects:

Optimum interaction with the design models.
Models are valid on a general basis.
Good balance between required input and accuracy.

In a IPSE GO project, you can use off-design models of the selected library units to build different calculation layers (datasets) of the process scheme. Usually, you first define a process model in the design mode, which feeds data to further off-design process models. In these off-design process models, you can simulate your process with different part loads.

Refer to the IPSE GO documentation, for more details about model refinement, dataset management, and off-design modeling.

Library Components

To get information about the component model available in the Advanced Power Plant Library, you should refer to the library on-line help .

The on-line help file can be accessed directly from IPSE GO.

3. Physical Properties and Chemical Compositions

This chapter explains how physical properties are handled in the Advanced Power Plant Library.

The first part of this chapter provides a list of all available chemical components, and the limitations that apply to each of them.

The second part explains how the physical properties are used in IPSE GO projects. It introduces the concept of compositions and explains how you deal with compositions in your projects.

Physical Properties

The Advanced Power Plant Library includes a database of physical properties for water and for a wide range of chemical components that might be used in the combustion system.

Although WATER and other chemical components are available in the same composition objects, you can only use either WATER or a mixture of the other components. It is not permitted to mix WATER with any other component. If you need water together with other components, use the defined component H2O instead.

Water and Steam

For calculating the properties of water and steam, you can choose one of the following formulations:

IAPWS_IF97. The IAPWS Industrial Formulation 1997 for the Thermodynamic Properties of Water and Steam ^[1].

When you are using IAPWS_IF97, the following limits for temperatures and pressures apply:

Limits for Water		min	max
Temperature [°C]		0.01	2000.0
Pressure [bar]	0.01 °C <= t <= 800 °C	0.1e-6	1000.0
	800 °C <= t <= 2000 °C	0.1e-6	100.0

Other Components

The physical properties of other components, rather than water and steam, are calculated with polynomials derived from the JANAF Thermochemical Tables ^[2]. All calculations are based on the assumption that the chemical components can be treated as ideal gases. The extent to which the ideal gas formulations yield acceptable accuracy depends on your specific application: While an inaccuracy of five percent might be unacceptable for a pure substance, it will be by far accurate enough if a mixture contains only a few percent of this substance. In practical usage, calculations for exhaust gas systems are always done using ideal gas formulations.

The following table lists the chemical components that are available in the physical properties database. The table also provides the temperature and the pressure range that is permitted by the system.

Variable	Component	Temperature [°C]		Pressure [bar]
		min	max	min	max
AR	Argon	-30.0	5726.85	0.1e-6	20.0
C2H6	Ethane	-30.0	5726.85	0.1e-6	35.0
C3H8	Propane	-25.0	5726.85	0.1e-6	35.0
CH4	Methane	-30.0	5726.85	0.1e-6	35.0
CO	Carbon monoxide	-30.0	5726.85	0.1e-6	100.0
CO2	Carbon dioxide	-30.0	5726.85	0.1e-6	35.0
H2	Hydrogen	-30.0	5726.85	0.1e-6	35.0
H2O	Steam (as ideal gas)	-30.0	5726.85	0.1e-6	30.0
H2S	Hydrogen sulfide	-20.0	5726.85	0.1e-6	100.0
N2	Nitrogen	-30.0	5726.85	0.1e-6	5.0
O2	Oxygen	-30.0	5726.85	0.1e-6	35.0
SO2	Sulfur dioxide	0.0	5726.85	0.1e-6	10.0

Compositions in a Process Model

In the Advanced Power Plant library, chemical compositions are not part of the streams that are available to connect the units. The streams reference global objects of type composition. This way, all streams with the same composition reference one single composition. This is illustrated by Figure 1.

Figure 1. Streams and composition

The advantage of this approach is that a stream can represent any flow of a medium that is available in the physical properties database. It does not matter if the stream represents the flow of steam, air, or natural gas. As a consequence, also the library components can be used on a general basis: The turbine model can be used for expanding steam as well as for expanding exhaust gas. This way, the number of necessary models is reduced, while the flexibility is increased.

Compositions are implemented as global objects. Compositions are defined in terms of their mass fractions. Each mass fraction is represented by a variable. If the variable CO2 of a composition is equal 0.5, this means that 50 percent of the mass of the composition is CO₂.

The next section explains how you can define a composition in IPSE GO.

Defining a Composition

To define a composition you do the following:

Select Objects › New Global Object to create the composition. Once you have created the composition, you can open it for editing.

When you prescribe a composition, always take care to prescribe it fully. You must enter the composition in terms of mass fractions. By definition, the sum of all mass fractions is equal to 1.0. Therefore, the following equation is part of the composition model:

\[\mu_{\text{WATER}} + \mu_{\text{AR}} + \ldots + \mu_{So_{2}} = 1.0 (1)\]

In order to define the composition fully, you must provide one setting less than the total number of components.

To prescribe a composition correctly:

Set to zero all mass fractions of chemical components that are not used.
Set all, except one, of the remaining mass fractions to the respective value.

Figure 2 shows the correct settings for a composition that contains 100% WATER. All components, except WATER, are set to zero. Since WATER is the only component that is not set, it is calculated from equation 1.

Figure 2. Composition window, correct settings for pure WATER

Figure 3 shows a frequent mistake that is made when defining the compositions. WATER is set to 1.0, but the remaining components are undefined.

Figure 3. Composition window, wrong settings for pure WATER

Using a Composition in a Stream

You have to select the composition for each stream of your process. However, instead of defining the used composition for each stream separately, you can also define it for a group of streams. In this case, all streams selected will use the same composition.

Defining a Composition for a Single Stream

To define the composition that is used in a stream:

Double click on the stream. IPSE GO opens the window for editing the data of that stream.
Select in the composition field the composition that you want to use.

Defining a Composition for a Group of Streams

To set the composition for a group of selected streams:

Select those streams for which you want to set the composition. It does not matter if you select other objects. If they do not contain references to compositions, they are simply ignored.
Select Objects › Set References. IPSE GO opens a window where you can select the type of reference that you want to set and the composition that you want to reference.
From the list of references select composition. Once you have made this selection, IPSE GO displays all available objects of type composition.
Select the composition that you want to use in the selected streams, and click on the Ok button to accept your choice.

Compositions and the System

IPSE GO requires that you define a correct mathematical system. If you use compositions incorrectly, you may create a system that is mathematically incorrect. The consequences are usually convergence problems.

Units that do not change Compositions

The majority of the units in the Advanced Power Plant Library do not change the chemical composition in a stream. They simply use the composition of the attached stream to calculate the required physical properties. See Figure 4 for an illustration.

Figure 4. Units that do not change compositions

Streams that are attached to a unit which does not change the composition must always reference the same composition!

Mixing Streams

If you mix two streams of different given compositions and of different given mass flows, the product is a third composition. The mixer model of the Advanced Power Plant Library takes into account the composition from the input streams and their respective mass flows, to calculate the mixed composition. Therefore, you must not prescribe the composition of the product stream. If you do so, you will create an over-determined system that will usually not converge.

However, if the same composition is used by the streams that are connected to the mixer, the mixer model takes into account this situation and delivers the same composition as a product. Hence, it is also possible to use mixers together with one single composition used by all streams (This is a very typical situation for steam cycles).

4. Examples

In this chapter you find step-by-step instructions for setting up several simple process schemes, using the Advanced Power Plant Library. These examples serve as a starting point for bigger projects.

Even if you dislike reading manuals, you are strongly encouraged to read through this section, since it provides you with the minimum of information required to use IPSE GO and the Advanced Power Plant Library!

Samples

For each unit a fully parameterized sample project exists which you can use to experiment with the settings.

To open a the sample project for a unit:

In the Icon bar select the icon of the unit for which you want to open the sample
Press F2
or
Right click on the icon and select the Open Sample command.
or
Click on the Open Sample icon.

Example 1: Stream

In this example, you will create a source and a sink that are connected by a stream. You will learn how you define a chemical composition. You will also see how PSE reacts on incorrect input. After you have created a new, empty project, you draw the scheme as shown in Figure 5.

Figure 5. Stream, flowsheet

To draw the scheme shown in Figure 5, you do the following:

Click on the source icon in the icon palette. When you move the cursor over the IPSE GO workspace to your project window, it takes the shape of the icon selected.
Click at the position where you want to place the source icon.
Place a sink icon in your project window, in the same way. Make sure that the sink icon remains selected.
Press Ctrl+R to rotate the sink icon counter clockwise by 90°.
Click on the box that marks the connection terminal of the source. By doing this you start the connection drawing mode.
Start drawing your connection. Click wherever you want the connection to have a corner.
Click on the box that marks the connection terminal of the sink. IPSE GO terminates the connection drawing mode, and attaches the connection to the sink.

IPSE GO automatically creates a name for each of the objects. To display the names, select View › Object Names.

By drawing the process scheme you have already set up the major part of the model. What is still missing is the information about working fluids and about numerical data. If you start the simulation now, you will receive the following error message:

After you have acknowledged the message by clicking on OK, PSE opens the data window of stream001, see Figure 6. (If you have not tried to run the calculation, you can open the data window for stream001, by double-clicking on the connection that you have drawn.)

Figure 6. Data window for stream001

You must now create a composition that the stream uses. You can create the composition directly from inside the data window of the stream.

To create a composition:

In the Composition row of the data window click on the New button. IPSE GO opens the window shown in Figure 7.
Select composition as the type of the global object, and enter WATER_STEAM in the name field. Click OK to create the new composition. PSE also automatically selects it as the composition of stream001, see figure Figure 8.

Figure 7. Dialog for creating new global objects

Figure 8. Data window of stream001 with selected composition

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You can now edit composition WATER_STEAM in order to define the composition. You can edit directly from inside stream001 which uses WATER_STEAM:

To edit the new composition from inside a stream:

In the Composition row of the data window of stream001 click Edit. IPSE GO opens the window shown in Figure 9.
Set all other chemical components besides WATER equal to zero. This means that your composition is pure water. To set a variable select the set option. PSE enables a field for entering data so that you can enter the respective value.
Close the composition window shown in Figure 9 by clicking OK to accept your settings.
Close the data window of stream001 shown in Figure 8 by clicking OK.

Figure 9. Data window of composition WATER_STEAM

If you closed to data window of stream001 you can edit WATER_STEAM directly by double clicking on the composition WATER_STEAM entry of the Object Manager, see Figure 10.

Figure 10. Object Manager

Try to start the calculation again. Select Calculation › Run Simulation. PSE will run through the calculation phase, and will return with the following message:

Click Yes. PSE opens the protocol where you find more details about the error that has occurred. The protocol first reports a warning:

%Warning: System undefined: 10 equations, 13 variables
1 groups found. Largest group contains 1 variables.

There is not enough information to solve the system. You have to prescribe three (13-10=3) more variables in order to make your system well defined. However, the solver tries to calculate as much as possible. You will also find an error message which contains more information. Click on the Next button of the protocol window to scroll to the error message:

%Error: System undefined. Degree of freedom: 3
Set one of the following variables to reduce the degree of freedom:
source001.p sink001.p source001.t stream001.v
stream001.p stream001.t stream001.h sink001.t
stream001.s
Set one of the following variables to reduce the degree of freedom:
sink001.mass stream001.mass source001.mass

If the difference between equations and variables is more than three, you have possibly set the composition incorrectly. Check the settings of your composition, before you prescribe the missing variables.

When a system is undefined, the solver analyses the system in order to identify those variables that can be set to reduce the degree of freedom. As a result of this setting analysis, it lists one or more groups of variables which are suitable settings. It is important to notice that you can choose one variable of each of the groups. Once you have made this choice, you need to run the solver again so that it can carry out a setting analysis for the new configuration.

Switch back to the project window or close the error protocol. PSE now displays a cross attached to the connection that shows the results obtained for the variables of the connection. A color scheme defines the status of the values displayed as follows:

Black

The value is a converged variable or it is a parameter.

Red

The variable did not converge.

Blue

The variable has not been calculated.

You can insert a reference cross to make it easier to identify the variables within your model.

To insert a reference cross:

Select Objects › Add Reference Cross. PSE opens a window displaying a list of all available connection models.
From the list of available connection models, choose stream.
Click OK. PSE inserts the reference cross in the lower left corner of the workspace. You can drag it to any other position of your project window.

Ex_01_02.pro ⇐

It is convenient to display the results of the setting analysis together with all settings that have already been made directly in the flowsheet:

To display settings and setting analysis results in the flowsheet:

Select View › Settings. PSE displays the flowsheet now as follows: The names of all variables that can be set are displayed in green.

Choose for this example the following values:

source

source001

10.0

bar

230.0

°C

mass

1.56

kg/s

To enter data for source001:

Double click on the source icon
or
Right click on the source icon and select from the menu that PSE displays the command Edit
or
double click on the source source001 entry of the Object Manager
or
right click on the source source001 entry of the Object Manager and select from the menu that PSE displays the command Edit. In all cases PSE opens the data window as shown in Figure 11.

Figure 11. Data window of source001

All variables that are valid settings are marked with a green frame. You can either set all 3 variables at once or add the settings step by step and allow the setting analysis to guide you in order to observe how it is working.

If you have already set pressure p and temperature t, but not yet the mass flow mass, PSE displays the flowsheet as follows:

The setting analysis clearly indicates that one of the mass flows needs to be set. Set mass in stream001 in order to make the process model defined.

Ex_01_03.pro ⇐

It is equally valid to set the mass flow at the sink, instead of at the source. If you set the mass flow at both, sink and source, the system is overspecified and PSE will report an error:

%Error: System overspecified
Remove one of the following settings to reduce overspecification:
source001.mass sink001.mass

When a system is overspecified, the solver analyses the system in order to identify those set variables that are in conflict with each other. As a result of this setting analysis, it lists one or more groups of set variables which are in conflict with each other. It is important to notice that you can remove the setting from one variable of each of the groups. If the system then is still overspecified, you need to run the solver again so that it can carry out a setting analysis for the new configuration.

If you display the settings, PSE will show the overspecification in the following way:

Conflicting settings are displayed in orange. Likewise, if you open the data window for source001, the setting of mass has a orange frame, indicating the this setting is in conflict with another one, see Figure 12.

Figure 12. Data window of source source001 with overspecification

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Example 2: Simple Steam Cycle

This example explains the steps that you must take to set up a model for the simple steam cycle shown in Figure 13. In this example, you will learn about specific aspects of closed cycles.

You will rarely start a new project from scratch. Usually, you modify existing projects according to your requirements. With this approach you can save a considerable amount of time, particularly for large projects.

In this example, you can reuse the composition from the previous project. Just open the first example, delete all (visible) objects and save it under a new name.

If you frequently use the same composition(s), create a project that only contains the composition(s). Whenever you need to create a new project with the already created composition(s), you can open this file and save it under a new name.

Figure 13. Simple steam cycle, flowsheet

Figure 13 shows the steam cycle that is modeled in this example. Note that the steam cycle is a closed loop. This requires some additional considerations. During the solution of the model equation the mass balances for each of the units is calculated, among other things. In a closed cycle, one of the mass balance equations is redundant, since it is automatically satisfied. Figure 14 explains this situation for a pair of pipes that are connected on both sides.

Figure 14. Mass balances for a closed cycle

In order to remove the redundant mass balance from a closed cycle model, you must insert a connection element. Using this connection element in the steam cycle of Figure 13, you obtain the model shown in Figure 15.

Figure 15. Model for a simple steam cycle

When you draw the process model, PSE creates a unique name for each of the objects that you add to the model. Start drawing the connections at the outlet of the connector and proceed clock-wise. PSE chooses the names as shown in Figure 15. To display the names, choose View › Object Names.

You must now define the compositions that are used. You can do it in the same way as it was done in the previous example. Open the data window for each stream and select the composition WATER_STEAM. Alternatively, you can set this composition for all streams at the same time.

To set the composition WATER_STEAM for a group of selected streams:

Select all streams for which you want to define the same composition.
Select Objects › Set References. PSE opens a window where you can select the type of reference that you want to set and the composition that you want to reference.
From the list of references select Composition (composition). Once you have made this selection, PSE displays all available objects of type composition. In this case only one object is available, WATER_STEAM.
Select WATER_STEAM and click OK to accept your choice.

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If you start the simulation now, you receive the following error message:

PSE has detected that you did not provide data for a parameter. Parameters are numerical values that always must be defined. Therefore, it is possible to check which parameters have not been defined. Acknowledge the message by clicking OK. PSE opens the data window for the respective unit, whose parameter is missing.

You have two options to provide the missing parameters:

Enter the parameters manually, by editing the unit data window.
Use values from the default value database.
To load default values from the default value database:
Select Objects › Load Default Values. PSE opens a window where you can select if you want to overwrite existing values.

If you have an object selected, PSE offers you to choose to load default values just for the selected object or for all objects of the project. Make the appropriate settings.

Click OK to load the default values.

EX_02_02.pro⇐

For most variables, PSE does not load settings for variables, since the settings depend on the system configuration and on your specific requirements. Default values for variables are usually loaded as estimates and not as settings. Yet some variables can also be configured in the model library that they are set whenever default values are loaded. In general, the user has to decide which variables are additionally set to make a system well-defined. For this task, the solver supports you with its setting analysis. If you start the simulation now, you receive the following error message:

Select YES to open a window displaying the protocol. The error message from the system is:

%Error: System undefined. Degree of freedom: 5
Set one of the following variables to reduce the degree of freedom:
stream001.v stream001.s stream001.t stream001.p
stream001.h stream005.v stream005.t stream004.v
stream004.s stream004.t stream005.p stream004.h
stream005.h boiler001.heat_input stream004.p stream005.s
stream001.mass stream005.mass turbine001.eta_s stream003.v
stream003.s stream003.h stream003.t stream002.h
stream002.mass stream004.mass turbine001.delta_hs stream002.v
stream002.s stream003.p shaft001.power stream003.mass
stream002.p generator001.power condenser001.q_trans stream002.t

To solve the system successfully you have to set 5 additional variables. You have the flexibility to choose the variables that are most appropriate for your particular problem. The selection of these variables requires a certain level of experience. However, you obtain support from the setting analysis, which suggests those variables that can be set.

For this example, choose the following variables:

stream

stream001

41.0

bar

440.0

°C

turbine

turbine001

eta_s

0.9

----

stream

stream002

0.05

bar

generator

generator001

power

1800

EX_02_03.pro⇐

Assume that you are interested in the thermal efficiency of the process. The definition that you are using is the following:

\[\eta = \frac{P_{\text{Generator}}}{Q_{\text{Boiler}}}\]

You can add a data frame that calculates the efficiency according to the equation above.

To calculate the thermal efficiency:

Select Objects › New Data Frame.
Choose that the data frame has 3 columns and one row.
Click in the workspace of your project window, to place the data frame.
The data frame has three cells. Select the first cell and type Efficiency.
Select the second cell.
Type "=". Then click on the Generator icon. PSE displays a list with all variables of the generator.
Select power from the list. PSE inserts the string generator001.power in the cell.
Type the division operator " / ".
Click on the boiler icon and select heat_input from the list of variables. PSE inserts the string boiler001.heat_input in the cell.
Select the third cell and type "[ – ]" to show that the calculated value is a dimensionless quantity.
Click into an empty area of the workspace. As soon as the data frame cell is deselected, the entered equation is evaluated and the result is displayed in the data frame.

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You can now try to prescribe different variables. You can, for example, prescribe the heat input to the cycle instead of the electrical power output. Do this by prescribing the variable heat_input for the boiler, instead of power for the generator.

Example 3: Steam Cycle with Deaerator

In this section the simple steam cycle is extended with a deaerator, see Figure 16. This example shows how you create a part-load model for the extended process scheme.

Figure 16. Steam cycle with deaerator

Design Model

The standard turbine model in the Advanced Power Plant Library does not contain bleed streams. To model a turbine with a bleed stream you use two turbine models and place a splitter between them. Using this approach you can model any number of bleed streams.

Very frequently it is not necessary to develop a model from scratch. It is more efficient to adjust existing models according to the current requirements. Take the model of Example 2: Simple Steam Cycle as basis for the new model. Before you start changing the model, you should save the project under a new name, to avoid the loss of the original model.

Disconnect the drain stream from the turbine so that you can insert a second turbine.

To disconnect a connection from a unit:

Press Crtl+F or select Objects › Free Connection. The cursor changes into a scissors symbol.
Click on the terminal where the drain stream is attached to the turbine. By doing so, you detach the connection from that terminal.
By double clicking on an unused area of the workspace, you create a free-end for this connection. The free end of a connection is marked by a circle.

Now you can carry on setting up the new scheme.

Place the second turbine icon and attach the connection to this icon. Click on the free end of the connection and you are again in the drawing mode of the connection. Draw all connections as shown in Figure 16.

You must now choose the compositions for all new streams and enter the parameters for the new units. You must also set sufficient variables to define the model. Set the pressure of the bleed stream.

Add the cooling water side of the condenser. The cooling water side is required in order to use the partload model of the condenser.

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Off-Design Model

The major difference between design and off-design or part-load calculations is that you need to use more detailed unit models for the latter. While it is possible to use the detailed models for calculating the off-design independently from a design calculation, it is more efficient to base off-design calculations on the design case:

The design case requires fewer input data. Results of the design case can be used as input for the off-design case.
A design model typically does not need initial estimates. The results of the design calculation can be used as initial estimates for off-design models.

For these reasons, an off-design calculation should always be based on a design simulation. You use PSE’s concept of datasets for establishing the relationship between design and off-design process models. Refer to the IPSEpro-PSE Documentation for more details about managing datasets.

The recommended procedure is the following:

Run a design simulation first in order to make the design results available.
Create an additional dataset in your project.
Select the appropriate off-design model for each component of the new dataset, and modify the settings accordingly.
Update the dataset with the data from the design case.
Run the simulation for the off-design dataset.
PSE provides an efficient mechanism to maintain consistency between design and off-design cases. You can create additional datasets that store the off-design model. If the design dataset is modified, you can easily update the off-design dataset.

You can carry out all dataset related tasks in the Dataset Manager, see Figure 17. To make a dataset the active one select it in the dataset manager.

Figure 17. Dataset Manager

To create an additional dataset in a PSE project:

In the Dataset Manager, right-click on the dataset that you want to be the source for the new new dataset
or
Choose Project › New Dataset. PSE uses the active dataset as the source for the new dataset.
PSE opens the window shown in Figure 18.
Enter the name for the new dataset and click OK. PSE creates the dataset and makes the new dataset the active one.

Figure 18. New Dataset window

Proceeding on the construction of the new process model, you have to change in the off-design dataset the component settings for the off-design model.

To change the model that is used for the condenser:

Double click on the condenser icon in the worksheet. PSE opens the dialog for editing the condenser’s data, see Figure 19.

Figure 19. Data window for the off-design model of the condenser

In the field Model choose the model condenser_pl. PSE opens a window with additional items of the condenser_pl model.
Click Load Defaults. PSE asks if you want to overwrite existing values.
Click Yes to close this message and to load the default values for the object.
Click Update Dataset. PSE updates the values of the condenser with the data from the source dataset. It now displays the data window of the condenser as shown in Figure 19.

EX_03_02.pro⇐

In the same way done for the condenser, change the data for the remaining models of the off-design dataset. Change the two turbine models to turbine_pl, and the boiler model to boiler_pl.

Do not forget to remove the respective settings in the modified objects. For example you will no longer be able to prescribe the pressure of the bleed stream. It is a frequent mistake to forget to remove some settings. If you run the calculation without removing the setting, the system will be over-determined, see Figure 20!

Figure 20. Off-design model with overspecification

EX_03_03.pro⇐

Frequently, it is useful to create more than one dataset. Datasets can then be organized hierarchically. Figure 21 shows a typical dataset hierarchy.

Figure 21. Dataset hierarchy

EX_03_04.pro⇐

Example 4: Combustion

In this section you will use the combustion chamber model to deal with the following issue:

Given ambient conditions and composition as well as conditions for a fuel gas, calculate the gas/air ratio you need to achieve a certain exhaust gas temperature.

In the APP_Lib you find two models for combustion chambers. The model combustor has to be used if the composition of the fuel is described by its elementary analysis. Usually this applies to liquid and solid fuels. The model combustor_c has to be used if the fuel is described by its chemical composition. That is the case for gaseous fuels.

In this example use the model combustor_c.

Figure 22. Combustion chamber

The first step is to define the composition. You need to create three compositions, AIR, FUEL and EXHAUST_GAS.

When you define compositions, do not forget that you must define all components in terms of their mass fractions (Not mole or volume fraction).

Use the following compositions:

Air

AIR

composition:

0.24

kg/kg

0.76

kg/kg

Natural Gas

FUEL

composition:

CH4

0.90

kg/kg

C2H6

0.08

kg/kg

C3H8

0.02

kg/kg

exhaust gas

EXHAUST_GAS

composition:

unknown

kg/kg

unknown

kg/kg

H2O

unknown

kg/kg

Use the following settings:

Air

mass flow

source001.mass

10.0

kg/s

pressure

source001.p

1.0

bar

temperature

source001.t

15.0

°C

Fuel

pressure

source002.p

5.0

bar

temperature

source002.t

°C

Combustion chamber

pressure drop of air

Combustor_c001.delta_p

0.01

bar

air ratio

Combustor_c001.lambda

3.0

EX_04_01.pro ⇐

If you start the system solution with this data, PSE will solve the model but will issue several warnings. Open the protocol and check the messages:

%Warning: Test condition for composition EXHAUST_GAS not satisfied:
tminWATER: "WATER < 0.0"
%Warning: Test condition for composition EXHAUST_GAS not satisfied:
tminAR: "AR < 0.0"
...

PSE checks, if the mass fractions are greater or equal 0.0. Due to numerical error some of the mass fractions are of magnitude -10^-16. While this is completely irrelevant for the solution, it triggers the warnings.

In order to remove these warnings, you should estimate the respective mass fractions to be 0.0. You can also set lower and upper limits for the respective mass fraction to be 0.0 and 1.0, respectively.

EX_04_02.pro ⇐

Example 5: Gas Turbine

Figure 23. Gas turbine model

In this section you will create a simple gas turbine model. You will create an object that represents the ambient conditions and link the air source to the ambient conditions.

Instead of starting a completely new project, you can modify the model stored in EX_04_02.pro as a starting point.

EX_05_01.pro ⇐

You will possibly want to prescribe the turbine inlet temperature instead of the air ratio. If you simply replace the setting of the air ratio with a setting of the temperature at the turbine inlet, PSE will not be able to solve the system. The built-in starting values are not accurate enough so that you must provide appropriate estimates.

While it is possible to enter estimates manually, you can create the estimates more efficiently in the following way:

To create estimates for EXHAUST_GAS:

Run the simulation.
Choose Calculation › Import Estimates. This replaces the default estimates with the results obtained in step 1.
Remove the setting for lambda and set the turbine inlet temperature at the relevant stream.

EX_05_02.pro ⇐

APP_Lib contains a global model ambient that represents the ambient conditions. You can create an ambient object and link all sources of ambient air to this object.

To create an ambient object:

Select Objects › New Global Object. PSE displays the list of available object types.
In the section global type select ambient.
Enter AMBIENT as the name for this global.
Click on the OK to create the AMBIENT object.

Make the following settings for the AMBIENT object:

Altitude

altitude

400.0

Temperature

°C

Relative humidity

phi

The system is now fully defined. However, the AMBIENT object is not yet used.

EX_05_03.pro ⇐

The next step is to link the gas turbine inlet to the ambient conditions.

If you use an ambient_source object, the composition of the AIR that leaves the object is defined. You must not set the composition in the AIR object.

To link the AMBIENT object with the gas turbine inlet:

Replace the source with an ambient_source.
In the AmbientConditions section of the ambient_source unit select AMBIENT.
Set the mass flow mass in the ambient_source. Do not set the temperature t and the pressure p because they are already defined in the AMBIENT object.
Open the AIR object and remove all settings.

EX_05_04.pro ⇐

Example 6: Heat Recovery Steam Generator

In this example, you will create the model of a heat recovery steam generator (HRSG) with a single pressure level.

You create the model by arranging a series of heat exchangers appropriately. This approach provides much higher flexibility than the one you can achieve with a single unit model of a HRSG. That is the reason why the Advanced Power Plant Library does not include a ready-to-use model of heat recovery steam generator.

The model of the heat recovery steam generator is shown in Figure 24. The model requires two compositions: one for the exhaust gas and one for water/steam. You can copy the compositions from the previous examples. See description to follow.

Figure 24. Heat recovery steam generator

To copy the composition EXHAUST_GAS:

Open example Ex_05_02.pro and run the calculation.
Select Calculation › Import Estimates. The results of the calculation are now stored in the EXHAUST_GAS object as estimates.
Still in the project of example 5, in the Object Manager select the composition EXHAUST_GAS.
Select Edit › Copy. Alternatively, you can press Ctrl+C.
Create a new project for the current example.
Select Edit › Paste or press Ctrl+V. This inserts the composition EXHAUST_GAS into the project.
In the Object Manager double click on the composition EXHAUST_GAS entry. PSE opens the data window of EXHAUST_GAS.
All values are estimates. Set all estimated values, except for N2, by selecting the set option. Click OK to finish.

EXHAUST_GAS is now ready for being used. Copy WATER_STEAM from example 1 or 2. You do not need to change any settings in the composition because they are already correct.

EX_06_01.pro ⇐

If you have little experience with heat recovery steam generators, you may have difficulties to specify appropriate parameters. As a consequence, you may obtain a model where the exhaust gas is reheated or that does not converge at all.

Instead of creating the complete heat recovery steam generator at once, it can be helpful if you split the water/steam side into three separate sections, representing the economizer, the evaporator with the drum, and the superheater.

Figure 25. Heat recovery steam generator with split water/steam side

Since the sections are not connected, you have a higher degree of freedom. For example, you can choose different mass flows to obtain a reasonable temperature profile for the exhaust gas side.

Depending of the values that you have chosen, the models may not converge in the evaporator. The reason is that you need a reasonable starting value for the enthalpy in the stream between evaporator and drum. Either load the default estimate or enter a value of about 1000 kJ/kg!

EX_06_02.pro ⇐

You should now adjust your data so that the results on both sides of the split streams match. Before you join the split streams, choose Calculation › Import Estimates. This ensures that your system uses good starting values for the iterations.

Whenever you join two separate sections by a stream, three settings become obsolete (e.g. mass, t, p) because the sections share the same condition where the stream connects them. Make sure that you adjust the settings appropriately. You can now join the split streams of your process model. You do this by deleting one stream and attaching the other one to the respective connector.

EX_06_03.pro ⇐

Similar to example 5, replace the sink with an ambient_sink. Do not set the pressure p because it is already defined in the AMBIENT object. Do not forget to remove all settings for the AIR object.

Example 7: Integrating Gas Turbine, Heat Recovery Steam Generator and Steam Cycle

In this example, you create a simplified model of a combined cycle.

Instead of creating the model from scratch, you will integrate the models of the previous examples into one single model. You will use the models from the examples 2, 5 and 6. Figure 26 shows the complete model of the combined cycle.

Figure 26. Combined cycle, created from other examples

The first step is to add the gas turbine model to the new project. You have two options to do that:

Open the gas turbine model EX_05_04.pro, and save it under a new name.
or
Open a new project and activate the project saved in EX_05_04.pro. Select all objects in EX_05_04.pro and copy them into the new project.

Since the new project will contain more components than the previous ones, you will need to change the scale or the page size.

Ex_07_01.pro ⇐

As the next step, you add the heat recovery steam generator that you have created in example 6.

To add the heat recovery steam generator to the current project:

Open project Ex_06_04.pro and select all objects in it.
Copy with Edit › Copy or by pressing Ctrl+C.
Activate the window that displays the new project.
Paste the copied objects via Edit › Paste, or by pressing Ctrl+V. PSE displays the following message:

Click No. The project now uses the EXHAUST_GAS composition of the gas turbine also for the heat recovery steam generator.
Connect the exhaust of the gas turbine with the heat recovery steam generator.

You have now again a fully working project.

EX_07_02.pro ⇐

As the last step, you add the steam cycle from example 2, saved as Ex_02_05.pro. Remove the boiler from the steam cycle and connect the rest to the heat recovery steam generator.

EX_07_03.pro ⇐

Example 8: Adding a Bypass to the Heat Recovery Steam Generator in the Combined Cycle Process

Now you will learn how to build a bypass for the heat recovery steam generator in the combined cycle process from the previous example and disable parts of the flowsheet. The bypass is displayed in Figure 27.

Figure 27. Combined Cycle Process with Bypass of HRSG

Create the bypass by inserting a splitter before and a mixer after the heat exchangers in the hot gas path. As the exhaust gas will experience a certain pressure drop in the bypass, a pipe model is inserted there. The global EXHAUST_GAS is also used in the bypass gas path and after the mixing point. Specify pressure drops and the mass flow in the bypass to make the model work. For numerical reasons it is advised to prescribe a small positive mass flow even if the bypass is not in use.

EX_08_01.pro ⇐

Yet there is also the possibilty to completely disable the bypass stream in the flowsheet. Then the model behaves and is calculated as if the bypass is not part of the flowsheet.

To disable the bypass gas path in the flowsheet:

Hold down Shift and select the two streams and the pipe unit with the mouse.
Choose Objects › Enable or press Ctrl+E.

Now the selected objects are disabled and are displayed in grey on the flowsheet. If you choose Objects › Enable or press Ctrl+E another time, the selected objects are enabled again.

Alternatively you can disable individual objects by unticking the option Enabled in the Data Input Dialog, as shown in Figure 28 for the pipe unit.

Figure 28. Pipe Enabled check box not ticked

If you run a calculation with the bypass objects disabled, the solver does not use the variables contained in these objects and solves the remaining flowsheet. The disabled objects do not show up in the calculation protocol.

Figure 29. Combined cycle process with bypass disabled

EX_08_02.pro ⇐

On the other hand, it is also possible just to use the bypass and disable the complete heat recovery steam generator and the steam turbine part of the flowsheet. The generator attached to the steam turbine via a shaft may remain enabled. In that case you have to manually set the shaft power to 0.0, otherwise the power output from the generator is undefined.

Figure 30. Combined cycle process with bypass only

For convenience, all three cases can be stored in three separate datasets within the same project file, as shown in Figure 31. The configuration with bypass only is contained in dataset 2 "Bypass only (steam cycle disabled)" of the example project.

Figure 31. Three separate independent datasets in the Dataset Manager

EX_08_03.pro ⇐

1. Wagner, W., Kruse, A.: Properties of Water and Steam, Springer-Verlag Berlin Heidelberg New York, 1998

2. JANAF Joint Army Navy Air Force Thermochemical Tables